System and method for controlling a variable valve actuation system to reduce delay associated with reactivating a cylinder

ABSTRACT

An engine control system includes a cylinder control module that deactivates and reactivates a cylinder of an engine based on a driver torque request while an ignition system associated with the engine is in an on position. A firing order module selectively adjusts a firing order of the engine based on a time when the cylinder is reactivated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 13/568,690 filed Aug. 7, 2012.

FIELD

The present disclosure relates to systems and methods for controlling avariable valve actuation system to reduce delay associated withreactivating a cylinder.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Internal combustion engines combust an air/fuel mixture within cylindersto drive pistons, which produces drive torque. Air enters the cylindersthrough intake valves. Fuel may be mixed with the air before or afterthe air enters the cylinders. In spark-ignition engines, spark initiatescombustion of the air/fuel mixture in the cylinders. Incompression-ignition engines, compression in the cylinders combusts theair/fuel mixture in the cylinders. Exhaust exits the cylinders throughexhaust valves.

A valve actuator actuates the intake and exhaust valves. The valveactuator may be driven by a camshaft. For example, the valve actuatormay be a hydraulic lifter that is coupled to the camshaft using apushrod or directly coupled to the camshaft. Alternatively, the valveactuator may actuate the intake and exhaust valves independent from acamshaft. For example, the valve actuator may be hydraulic, pneumatic,or electromechanical, and may be used in a camless engine and/or acamless valvetrain.

SUMMARY

A system according to the principles of the present disclosure includesa cylinder control module and a valve control module. The cylindercontrol module deactivates and reactivates a cylinder of an engine basedon a driver torque request while an ignition system associated with theengine is in an on position. The valve control module selectivelyadjusts a period for which at least one of an intake valve and anexhaust valve of the cylinder are opened based on a first time when thecylinder is reactivated.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram illustrating an example enginesystem according to the principles of the present disclosure;

FIG. 2 is a functional block diagram illustrating an example enginecontrol system according to the principles of the present disclosure;and

FIG. 3 is a flowchart illustrating an example engine control methodaccording to the principles of the present disclosure.

DETAILED DESCRIPTION

An engine control system may deactivate one or more cylinders of anengine to improve fuel economy. When a cylinder is deactivated, fueldelivery to the cylinder and/or spark generation in the cylinder may bestopped. In addition, an intake valve and an exhaust valve of thecylinder may be closed to trap exhaust gas in the cylinder. Trappingexhaust gas in the cylinder reduces pumping losses associated withpumping air into and out of the cylinder and thereby improves fueleconomy.

When the cylinder is reactivated, the exhaust valve may be opened tovent exhaust gas from the cylinder. The exhaust valve may be closed whena piston in the cylinder is at its topmost position, referred to as topdead center (TDC). The exhaust valve may be opened for a fixed periodeach engine cycle. For example, if the exhaust valve is opened using avalvetrain that is driven by a camshaft of the engine, the period whenthe exhaust valve is opened may depend on rotation of the camshaft. Ifthe cylinder is reactivated during the period when the exhaust valvewould have been open if it was not deactivated, the exhaust valve maynot be opened until the exhaust stroke of the next engine cycle. Inturn, the torque response of the engine may be delayed.

A system and method according to the principles of the presentdisclosure opens an exhaust valve of a cylinder when the cylinder isreactivated if a period before a piston in the cylinder reaches TDC issufficient to vent exhaust gas from the cylinder. The period when theexhaust valve is opened may be varied using a camless valvetrain. Thus,the exhaust valve may be opened at a later time and for a shorter periodwhen the cylinder is reactivated. For example, the exhaust valve may beopened during the period when the exhaust valve would have been open ifit was not deactivated.

If the period before the piston reaches TDC is not sufficient to ventexhaust gas from the cylinder, the firing order of the engine may beadjusted. For example, the spark timing of the reactivated cylinder maybe advanced by 360 degrees without adjusting the spark timing of theother cylinders in the engine. The exhaust valve may then be openedduring the next piston stroke. Opening the exhaust valve when thecylinder is reactivated, or during the next piston stroke, instead ofwaiting for the exhaust stroke of the next engine cycle improves thetorque response of the engine.

Referring now to FIG. 1, an example implementation of an engine system100 includes an engine 102 that combusts an air/fuel mixture to producedrive torque for a vehicle based on driver input from a driver inputmodule 104. Air is drawn into the engine 102 through an intake system108. In various examples, the intake system 108 includes an intakemanifold 110 and a throttle valve 112. In various examples, the throttlevalve 112 includes a butterfly valve having a rotatable blade. An enginecontrol module (ECM) 114 controls a throttle actuator module 116, whichregulates opening of the throttle valve 112 to control the amount of airdrawn into the intake manifold 110.

Air from the intake manifold 110 is drawn into cylinders of the engine102. While the engine 102 may include multiple cylinders, forillustration purposes a single representative cylinder 118 is shown. Invarious examples, the engine 102 includes 2, 3, 4, 5, 6, 8, 10, or 12cylinders. The ECM 114 deactivates one or more cylinders of the engine102 under certain engine operating conditions to improve fuel economy.The ECM 114 may deactivate all of the cylinders, or less than all of thecylinders, while an ignition system 120 is in an on position. The ECM114 starts and stops the engine 102 based on input received from theignition system 120 via the driver input module 104.

The engine 102 may operate using a four-stroke cycle. The four strokes,described below, are named the intake stroke, the compression stroke,the combustion stroke, and the exhaust stroke. During each revolution ofa crankshaft (not shown), two of the four strokes occur within thecylinder 118. Therefore, two crankshaft revolutions are necessary forthe cylinder 118 to experience all four of the strokes.

During the intake stroke, air from the intake manifold 110 is drawn intothe cylinder 118 through an intake valve 122. The ECM 114 controls afuel actuator module 124, which regulates fuel injection to achieve adesired air/fuel ratio. Fuel may be injected into the intake manifold110 at a central location or at multiple locations, such as near theintake valve 122 of each of the cylinders. In various implementations(not shown), fuel is injected directly into the cylinders or into mixingchambers associated with the cylinders. The fuel actuator module 124 mayhalt injection of fuel to cylinders that are deactivated.

The injected fuel mixes with air and creates an air/fuel mixture in thecylinder 118. During the compression stroke, a piston (not shown) withinthe cylinder 118 compresses the air/fuel mixture. The engine 102 may bea compression-ignition engine, in which case compression in the cylinder118 ignites the air/fuel mixture. Alternatively, the engine 102 may be aspark-ignition engine, in which case a spark actuator module 126energizes a spark plug 128 in the cylinder 118 based on a signal fromthe ECM 114, which ignites the air/fuel mixture. The timing of the sparkmay be specified relative to the time when the piston is at its topmostposition, referred to as top dead center (TDC).

The spark actuator module 126 may be controlled by a timing signalspecifying how far before or after TDC to generate the spark. Becausepiston position is directly related to crankshaft rotation, operation ofthe spark actuator module 126 may be synchronized with crank angle. Invarious implementations, the spark actuator module 126 may haltprovision of spark to deactivated cylinders.

Generating the spark may be referred to as a firing event. The sparkactuator module 126 is able to vary the timing of the spark for eachfiring event. The spark actuator module 126 is capable of varying thespark timing for a next firing event when the spark timing signal ischanged between a last firing event and the next firing event. Invarious implementations, the spark actuator module 126 varies the sparktiming relative to TDC by the same amount for all of the cylinders inthe engine 102.

During the combustion stroke, the combustion of the air/fuel mixturedrives the piston down, thereby driving the crankshaft. The combustionstroke may be defined as the time between the piston reaching TDC andthe time at which the piston returns to bottom dead center (BDC). Duringthe exhaust stroke, the piston begins moving up from BDC and expels thebyproducts of combustion through an exhaust valve 130. The byproducts ofcombustion are exhausted from the vehicle via an exhaust system 134.

The intake valve 122 may be actuated using an intake valve actuator 140,while the exhaust valve 130 may be actuated using an exhaust valveactuator 142. In various implementations, the intake valve actuator 140may actuate multiple intake valves (including the intake valve 122) forthe cylinder 118. Similarly, the exhaust valve actuator 142 may actuatemultiple exhaust valves (including the exhaust valve 130) for thecylinder 118. Additionally, a single valve actuator may actuate one ormore exhaust valves for the cylinder 118 and one or more intake valvesfor the cylinder 118.

The intake valve actuator 140 and the exhaust valve actuator 142 actuatethe intake valve 122 and the exhaust valve 130, respectively,independent from a camshaft. In this regard, the valve actuators 140,142 may be hydraulic, pneumatic, or electromechanical and may be used ina camless valvetrain, and the engine 102 may be a camless engine. Aspresently shown, the valve actuators 140, 142 are hydraulic, and ahydraulic system 144 supplies hydraulic fluid to the valve actuators140, 142.

The hydraulic system 144 includes a low-pressure pump 146, ahigh-pressure pump 148, and a reservoir 150. The low-pressure pump 146supplies hydraulic fluid from the reservoir 150 to the high-pressurepump 148 through a supply line 152. The high-pressure pump 148 supplieshydraulic fluid from the supply line 152 to the valve actuators 140,142. The low-pressure pump 146 may be an electric pump, and thehigh-pressure pump 148 may be driven by the engine 102 using, forexample, a belt.

A valve actuator module 158 controls the intake valve actuator 140 andthe exhaust valve actuator 142 based on signals from the ECM 114. Thevalve actuator module 158 may control the intake valve actuator 140 toadjust the lift, duration, and/or timing of the intake valve 122. Thevalve actuator module 158 may control the exhaust valve actuator 142 toadjust the lift, duration, and/or timing of the exhaust valve 130.

A pump actuator module 160 controls the low-pressure pump 146 and thehigh-pressure pump 148 based on signals from the ECM 114. The pumpactuator module 160 may control the low-pressure pump 146 to adjust thepressure of hydraulic fluid supplied to the high-pressure pump 148. Thepump actuator module 160 may control the high-pressure pump 148 toadjust the pressure of hydraulic fluid supplied to the valve actuators140, 142.

The engine system 100 may measure the position of the crankshaft using acrankshaft position (CKP) sensor 180. The temperature of the enginecoolant may be measured using an engine coolant temperature (ECT) sensor182. The ECT sensor 182 may be located within the engine 102 or at otherlocations where the coolant is circulated, such as a radiator (notshown). The pressure within the intake manifold 110 may be measuredusing a manifold absolute pressure (MAP) sensor 184.

The mass flow rate of air flowing into the intake manifold 110 may bemeasured using a mass air flow (MAF) sensor 186. In variousimplementations, the MAF sensor 186 may be located in a housing thatalso includes the throttle valve 112. The position of the throttle valve112 may be measured using one or more throttle position sensors (TPS)190. The ambient temperature of air being drawn into the engine 102 maybe measured using an intake air temperature (IAT) sensor 192.

The lift of the intake valve 122 may be measured using an intake valvelift (IVL) sensor 194. The lift of the exhaust valve 130 may be measuredusing an exhaust valve lift (EVL) sensor 196. The valve lift sensors194, 196 may output the lift of the intake and exhaust valves 122, 130to the valve actuator module 158, as shown, and the valve actuatormodule 158 may output the lift of the intake and exhaust valves 122, 130to the ECM 114. Alternatively, the valve lift sensors 194, 196 mayoutput the lift of the intake and exhaust valves 122, 130 directly tothe ECM 114. The ECM 114 may use signals from the sensors to makecontrol decisions for the engine system 100.

Referring now to FIG. 2, an example implementation of the ECM 114includes a driver torque module 202, a cylinder control module 204, anda firing order module 206. The driver torque module 202 determines adriver torque request based on driver input from the driver input module104. The driver input may be based on a position of an acceleratorpedal. The driver input may also be based on cruise control, which maybe an adaptive cruise control system that varies vehicle speed tomaintain a predetermined following distance. The driver torque module202 may store one or more mappings of accelerator pedal position todesired torque, and may determine the driver torque request based on aselected one of the mappings.

The cylinder control module 204 may deactivate one or more cylinders ofthe engine 102, such as the cylinder 118. In various implementations, apredefined group of cylinders are deactivated jointly. The cylindercontrol module 204 may instruct a valve control module 208 to close theintake and exhaust valves of deactivated cylinders. The valve controlmodule 208 outputs a signal to the valve actuator module 158 to open orclose the intake valve 122 and/or the exhaust valve 130.

The valve control module 208 may time the closing of the intake valve122 and the exhaust valve 130 to trap exhaust gas in the cylinder 118while the cylinder 118 is deactivated. In various examples, the valvecontrol module 208 closes the intake valve 122 after the cylinder 118completes an intake stroke and closes the exhaust valve 130 before thecylinder 118 completes an exhaust stroke. Trapping exhaust gas in acylinder when the cylinder is deactivated reduces pumping losses of thecylinder.

The cylinder control module 204 instructs a fuel control module 210 tostop providing fuel to deactivated cylinders. The fuel control module210 outputs a signal to the fuel actuator module 124 to adjust fueldelivery to the cylinder 118. The cylinder control module 204 may or maynot instruct a spark control module 212 to stop providing spark todeactivated cylinders. In various implementations, the spark controlmodule 212 only stops providing spark to a cylinder once any fuel/airmixture already present in the cylinder has been combusted. The sparkcontrol module 212 outputs a signal to the spark actuator module 126 toadjust spark generation in the cylinder 118.

The cylinder control module 204 reactivates the cylinder 118 when thedriver torque request is greater than a first torque, which may bepredetermined. When the driver torque request is less than or equal tothe first torque, the cylinder control module 204 instructs a throttlecontrol module 214 to adjust the throttle valve 112 to satisfy thedriver torque request. The throttle control module 214 outputs a signalto the throttle actuator module 116 to adjust the throttle valve 112.

In various implementations, the firing order module 206 adjusts thefiring order of the engine 102 and/or the valve control module 208adjusts the valve timing of the engine 102 only when the driver torquerequest is greater than a second torque. The cylinder control module 204may determine whether the driver torque request is greater than thesecond torque. The second torque may be predetermined and may correspondto a percentage (e.g., 90 percent) of wide open throttle.

The valve control module 208 may adjust valve timing during the currentengine cycle based on a first time when the cylinder 118 is reactivated.The valve control module 208 opens the intake and exhaust valves 122,130 normally when a crank angle corresponding to the first time isgreater than or equal to a first angle. The crank angle may be specifiedin number of degrees before TDC. The cylinder control module 204 maydetermine the crank angle based on input from the CKP sensor 180.

When opening the exhaust valve 130 normally, the valve control module208 opens the exhaust valve 130 for a first period. When a period beforethe piston reaches TDC is less than the first period, the valve controlmodule 208 may not open the exhaust valve 130 until the next enginecycle. The cylinder control module 204 may determine the period beforethe piston reaches TDC based on the crank angle and engine speed. Enginespeed is determined based on input from the CKP sensor 180. When thevalve control module 208 opens the intake valve 122 normally, the valvecontrol module 208 opens the intake valve 122 before the exhaust valve130 closes.

When the crank angle corresponding to the first time is less than thefirst angle but greater than a second angle, the valve control module208 opens the exhaust valve 130 for a second period that is less thanthe first period. In addition, the valve control module 208 does notopen the intake valve 122 until the exhaust valve 130 closes to preventvalve overlap. Pressure in the cylinder 118 may be high due to theshortened period during which exhaust gas is vented from the cylinder118. Preventing valve overlap ensures that exhaust gas is not forcedthrough the intake valve 122. After adjusting valve timing based on thefirst time, the valve control module 208 opens the intake and exhaustvalves 122, 130 normally during the next engine cycle.

When the crank angle corresponding to the first time is less than orequal to the second angle, the firing order module 206 adjusts thefiring order of the engine 102. The firing order module 206 may advancethe spark timing of the cylinder 118 by 360 degrees without advancingthe spark timing of other cylinders in the engine 102. The firing ordermodule 206 may notify the cylinder control module 204 when the firingorder module advances the spark timing of the cylinder 118 by 360degrees. In turn, the valve control module 208 and the fuel controlmodule 212 may adjust valve timing and fuel injection timing,respectively, based on the advanced spark timing.

Thus, if the period prior to TDC is less than the first period, thevalve control module 208 does not wait nearly a full engine cycle beforeopening the exhaust valve 130. Instead, the valve control module 208opens the exhaust valve 130 during the next piston stroke. The valvecontrol module 208 opens the exhaust valve 130 for the first period andcloses the exhaust valve 130 at or near TDC of the next piston stroke.

Referring now to FIG. 3, a method for reducing delay in the torqueresponse of an engine associated with reactivating a cylinder of theengine begins at 302. At 304, the method determines whether the cylinderis deactivated. If the cylinder is deactivated, the method continues at306. Otherwise, the method continues at 308.

At 306, the method determines whether a driver torque request is greaterthan a first torque. The driver torque request may be determined basedon driver input such as an accelerator pedal position or a cruisecontrol setting. The first torque may be predetermined. If the drivertorque request is greater than the first torque, the method continues at310. Otherwise, the method continues at 312. At 312, the methodsatisfies the driver torque request by adjusting a position of athrottle valve.

At 310, the method determines whether the driver torque request isgreater than a second torque. The second torque may be predetermined andmay be a percentage (e.g., 90 percent) of wide open throttle. If thedriver torque request is greater than the second torque, the methodcontinues to 314. Otherwise, the method continues to 316.

At 316, the method determines whether a crank angle corresponding to afirst time when the cylinder is reactivated is greater than or equal toa first angle. The crank angle may represent an amount of crankshaftrotation before a piston in the cylinder reaches TDC. If the crank angleis greater than or equal to the first angle, the method continues at318. Otherwise, the method returns to 304. At 318, the method opens anexhaust valve of the cylinder for a first period. The first angle andthe first period may be predetermined and may correspond to normaloperation. If the crank angle is less than the first angle, the methodmay open the exhaust valve during an exhaust stroke of the next enginecycle.

At 314, the method determines whether the crank angle is greater than asecond angle. If the crank angle is greater than the second angle, themethod continues at 320. Otherwise, the method continues at 322. At 320,the method opens the exhaust valve for a second period that is less thanthe first period. The second period may be predetermined based on anamount of time required to vent exhaust gas from the cylinder. At 324,the method delays opening the intake valve until after the exhaust valveis closed to prevent valve overlap.

At 322, the method adjusts a firing order of the engine. For example,the method may advance the spark timing of the cylinder by 360 degreeswithout advancing the spark timing of other cylinders in the engine. Themethod may adjust the valve timing and the fuel injection timing of thecylinder based on the advanced spark timing.

At 308, the method determines whether the firing order of the engine isout of sequence. The firing order of the engine may be out of sequencewhen the spark timing of the cylinder is advanced by 360 degrees. Whenthe firing order of the engine is out of sequence, the method continuesat 326. Otherwise, the method returns to 304. By opening the exhaustvalve for the second period or advancing the spark timing of thecylinder by 360 degrees, the method improves the torque response of theengine.

At 326, the method determines whether the driver torque request isdecreasing. If the driver torque request is decreasing, the methodcontinues at 328. Otherwise, the method returns to 304. At 328, themethod skips a firing event and readjusts the firing order of the engineso that the firing order is not out of sequence. The method may readjustthe firing order of the engine by retarding the spark timing of thecylinder by 360 degrees.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. For purposes of clarity, thesame reference numbers will be used in the drawings to identify similarelements. As used herein, the phrase at least one of A, B, and C shouldbe construed to mean a logical (A or B or C), using a non-exclusivelogical OR. It should be understood that one or more steps within amethod may be executed in different order (or concurrently) withoutaltering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable hardware components that provide the described functionality;or a combination of some or all of the above, such as in asystem-on-chip. The term module may include memory (shared, dedicated,or group) that stores code executed by the processor.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors. In addition, some or all code from a single module may bestored using a group of memories.

The apparatuses and methods described herein may be implemented by oneor more computer programs executed by one or more processors. Thecomputer programs include processor-executable instructions that arestored on a non-transitory tangible computer readable medium. Thecomputer programs may also include stored data. Non-limiting examples ofthe non-transitory tangible computer readable medium are nonvolatilememory, magnetic storage, and optical storage.

What is claimed is:
 1. An engine control system comprising: a cylinder control module that deactivates and reactivates a cylinder of an engine based on a driver torque request while an ignition system associated with the engine is in an on position; and a firing order module that selectively adjusts a firing order of the engine based on a crank angle of the engine at a time when the cylinder is reactivated.
 2. The engine control system of claim 1, wherein the firing order module adjusts the firing order when the driver torque request is greater than a predetermined torque.
 3. The engine control system of claim 1, wherein the firing order module advances spark in the cylinder by N degrees when the crank angle is less than a predetermined angle.
 4. The engine control system of claim 3, wherein the crank angle corresponds to a piston position at the time relative to top dead center, and N is an integer greater than
 1. 5. The engine control system of claim 4, wherein N is
 360. 6. A method for controlling an engine, comprising: deactivating and reactivating a cylinder of the engine based on a driver torque request while an ignition system associated with the engine is in an on position; and selectively adjusting a duration of a period for which at least one of an intake valve and an exhaust valve of the cylinder are opened based on a first time corresponding to a crank angle of the engine when the cylinder is reactivated relative to top dead center; opening the exhaust valve at a second time that is based on the first time opening the exhaust valve when the cylinder is reactivated if the crank angle is greater than a first predetermined angle; and adjusting a firing order of the engine based on the first time.
 7. The method of claim 6, further comprising adjusting the firing order when the driver torque request is greater than a predetermined torque.
 8. The method of claim 6, further comprising advancing spark in the cylinder by N degrees when the crank angle is less than or equal to the predetermined angle, wherein N is an integer greater than
 1. 9. The method of claim 8, wherein N is
 360. 